That was the unfortunate case last December for the 49ers, when a triceps injury kept Smith out of their 42-13 loss to the Seahawks, ending the defensive mainstay's streak of 185 consecutive starts.

"It was a big factor," Willis said of Smith's absence. "Justin, to me, is one of the best defensive players in the league. Anytime he's not out there, we miss him.

"But we've got him back now. We know he's going to be a difference-maker, as always."

Smith looks at full strength entering his 13th season. His left-arm injury is in the past, and his focus instead is on a Seahawks offense that parlays quarterback Russell Wilson's mobility and Marshawn Lynch's rushing yards.

The San Francisco 49ers' Ray McDonald (91) and Justin Smith, (94) help force a fumble by the Green Bay Packers' Eddie Lacy (27) in their NFL game played at Candlestick Park in San Francisco, Calif., on Sunday, Sept. 8, 2013. (Dan Honda/Bay Area News Group)
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"I just try not to think about it," Smith said of his arm. "If something happens again, something happens again. I'm not trying to gauge it every play."

Smith should be an every-down factor against the Seahawks, who last season scored five touchdowns against a 49ers defense that started Ricky Jean-Francois in place of Smith.

So is Smith more valuable in stopping Lynch or getting a pass rush on Wilson?

"Both," defensive coordinator Vic Fangio said. "Justin is a complete player. He's not one-dimensional. He helps us both defend the run and the pass."

Seahawks offensive coordinator Darrell Bevell agreed that Smith makes a "huge" difference in the 49ers' attack, and not just as a veteran leader.

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"He's very savvy with his technique," Bevell told Seahawks.com. "He gets great push. He does some really nice work with the games with Aldon (Smith)."

Bevell noted how Aldon Smith and Ahmad Brooks occasionally switched sides against the Packers -- a rarity last season -- and that Justin Smith's help will "free up" whomever is next to him.

Getting to Wilson will be a challenge, however. His ability to slip out of the pocket and escape danger helped key the Seahawks' rout of the 49ers in their last meeting.

Justin Smith (94) of the San Francisco 49ers catches a breather during drills at the team's training camp in Santa Clara, Calif., on Thursday, August 1, 2013. (Karl Mondon/Bay Area News Group)

"He's just a fast, quick, elusive guy," Justin Smith said. "You've just got to mind your rush lanes, because he'll squeeze out and get rolling on you.

"We don't have a pocket-passer statue that we practiced against, so we've been prepared for that. (Colin) Kaepernick, when you practice against him, he gives you a good look at that."

Rookie B.J. Daniels is mimicking Wilson on the scout team this week. Both are 5-foot-11 quarterbacks with darting speed and accurate arms.

Justin Smith's nonstop motor could pay dividends against a quarterback such as Wilson, who creates what Fangio termed a "second play" once the scripted one breaks down.

The Seahawks' offensive style certainly differs from the Green Bay Packers' pass-oriented attack that the 49ers defeated in Sunday's season opener. Look for the 49ers to play more of their base defense of three linemen, four linebackers.

That means nose tackle Ian Williams will see the most action of his neophyte career, with Justin Smith as a trusty wingman. Williams, who estimated he played about four snaps at nose tackle in the opener, learned quickly in camp what it's like to play next to Smith.

"He's a beast out there," Williams said. "He just wrecked shop. That's what he does."